Process for producing nitroparaffins by reacting an alkyl nitrite with a nitrating agent



bon chain length, e.g.

United States Patent 3,209,038 PROCESS FOR PRODUCING NTI'ROPARAFFENS BY REACTING AN ALKYL NITRITE WITH A NL- The present invention relates to a novel process for the preparation of nitroparaffins. More particularly, this application pertains to the preparation of nitroparafiins by nitration of alkyl nitrites, e.g., n-propyl nitrite, iso-propyl nitrite, and the like, especially under such conditions as to selectively produce desired nitroparafiins of lower carnitromethane and nitroethane.

It has been known for many years that nitroparafiins can be produced by reacting parafiins with a nitrating agent such as nitric acid or an oxide of nitrogen in the vapor phase. In this known process, however, although the rate of nitration is fast, the rate of oxidation is also very fast, and in fact, to avoid the latter becoming excessive and a consequent risk of explosion, it is not practical to employ a volume ratio of parafiin to nitrating agent of less than about 3 to 1. Although considerable progress has been made in the synthesis of nitroparaflins during the past decade, this progress has resulted in an increase in the conversion of the paraifin under conditions that have not resulted in enhanced production of particular nitroparaflins. For example, a mixture of nitromethane, nitroethane, l-nitropropane and 2-nitropropane is obtained from the nitration of propane with suitable nitrating agents. In addition, partial oxidation products such as aldehydes, ketones and acids are obtained under such conditions thereby presenting a separation problem and sacrifice in ultimate yield of nitroparafiin.

The present invention is directed, in contrast to these known processes, to a process for the preparation of nitroparaflins by nitration of the alkyl nitrites to provide great er selectivity in the production of desired nitroparaflins, for example, nitromethane and nitroethane from propyl nitrite. For instance, in the nitration of the alkyl nitrites, far fewer nitroalkanes are produced than if the corresponding alkane had been nitrated according to the prior art. Accordingly, separation of the nitroparaflin products is less difiicult. Moreover, the alkyl nitrite can be selected to provide desired nitroparaffins.

The present process generally involves reaction of an alkyl nitrite and a nitrating agent at a relatively high temperature. Under the reaction conditions which characterize the present process, as are described in detail hereinafter, an appreciable reaction occurs to produce nitroparaflins selectively.

The nitrating agents used in the present process include nitric acids, generally 40 to 70 percent nitric acids (specific gravity about 1.25 to 1.42) and oxides of nitrogen higher than NO such as N0 One of the most advantageous factors of the present invention is the mole ratio of the nitrite to the nitrating agent which can be low, e.g., approximately 1:1, as well as 30:1 or more, for instance, to produce nitroparafiins selectively. Generally a ratio of from about 0.5 :1 to 2.5 :1 is preferred, and a ratio of from about 0.711 to about 1.2:1 is optimum.

The reaction temperatures employed are those suflicient to effect reaction between the alkyl nitrite and the nitrating agent. In general, with nitric acid, a temperature of at least 250 or 350 C. and up to 450 C., or more, preferably 375 to 425 C., is used. If the nitrating agent to be used is N0 the temperature is generally from about 240 to 325 C. At temperatures much in excess of 325 C., i.e., about 361 C. the reactants may be oxidized, i.e., burned-up, when the N0 nitrating agent is used. The present process is generally carried out at about atmospheric pressure although an increased pressure, e.g., up to about 15 atmospheres or more, may be used if desired.

The reaction time is dependent upon the temperature used. At higher temperatures, a shorter time can be used, which is preferred since it is desired to avoid production of partial oxidation products such as ketones, etc. At any temperature there is an optimum contact time and any additional increase in the contact time tends to increase the amount of oxidation products relative to the amount of nitration products. Generally a contact time of from about 0.01 to 20 seconds may be used for the above temperatures.

The alkyl nitrites which may be nitrated in the process of the present invention include those nitrites the alkyl group of which has from two up to about eight to ten carbon atoms. Specific examples of such alkyl nitrites include ethyl nitrite, n-propyl nitrite, isopropyl nitrite, nbutyl nitrite, n-amyl nitrite, n-hexyl nitrite, etc. In contrast to the nitration of a paraifin as known heretofore which requires the presence of a hydroxyl radical to initiate the same by removing a hydrogen, the present reaction is believed to be a thermal splitting of the alkyl nitrite at the carbon atoms having the nitrite radical attached, thus not requiring the presence of a hydroxyl radical, to form the specific nitroparaflins of a lower carbon atom range than the alkyl nitrite in addition to an aldehyde. n-Propyl nitrite, for example, when nitrated according to the present process, splits to form nitromethane, nitroethane and formaldehyde whereas isopropyl nitrite splits to form nitromethane and acetaldehyde.

The alkyl nitrites used in the present invention are easily obtained commercially and provide an inexpensive starting material for the production of the nitroparaflins. The nitrites may be produced, for example, by the nitrosation of lower alkyl alcohols with nitrous acid in the presence of water.

In carrying out the novel process of the present invention it is preferable to introduce the alkyl nitrite and nitrating agent as a mixture into a reactor with the mixture being preheated to a temperature below that at which the alkyl nitrite and nitrating agent Will react. Accordingly,

.the nitrating agent, when nitric acid, may be pre-heated to a temperature of from about 200 to 260 C. and mixed with the alkyl nitrite in such proportions as to provide a molar ratio such as those described above, for instance, prior to introduction into the reactor. Of course, the nitrating agent and alkyl nitrite to be nitrated may be introduced into the reactor through separate streams.

The reactor can be heated by a molten salt to maintain an even temperature in the reactor by absorbing the heat of reaction in order to insure a good yield of the desired nitroparafiins. The choice of salt to be employed as the molten medium depends upon the choice of the temperature at which the reaction is to be carried out. It

is generally preferred to employ a eutectic mixture of potassium and sodium nitrates. Since such mixture can be maintained in the molten state throughout a temperature range of about 260 to 550 C. without solidification or decomposition. Other single salts or mixture of salts can obviously be employed, as, for example, a eutectic mixture of sodium, potassium, and lithium nitrates which has a melting point below 200 C., i.e. about Since the reaction between the nitrite and the nitrating agent is exothermic, it is also possible to spray one or both of the reactants as a liquid into a reaction zone and utilize the heat of reaction to vaporize the liquid reactant 3 or reactants. A reactor of this type may operate substantially adiabatically.

Since the reaction product of the nitrating agent and alkyl nitrite is in the gaseous phase it can easily be re- In an apparatus similar in all essential respects to that described in Example I, the following alkyl nitrites were nitrated with nitric acid and nitrogen dioxide according moved from the reaction zone by means of a vapor exit 5 and thereafter condensed. The condensed products form to the fOhOWlhg tablean aqueous layer and an oily nitroparafiin layer which may.be easlly separated from the aqueous layer by com Alkyl nitrite Nitrating Nitroparailin produced vention methods. agent The following examples are provided hereinafter in order to further illustrate the present invention without, nlitrittegnh r ngs. 1i ron1e3mne N \1 11- u n1rie -1 irome 1a11e,ni roe iane, however, l1m1t1ng the same. I A y H O Nam1mt0pr0pane I X X nm lnitritefln N itrometiane,nitroetiane, EXAMPLE I 3 3 Lnitropropane,l-n-butane. XX n-lIexylnitrite. NO2 Nitromethane,nitroethane, n-Propyl nitrite at ambient temperature was allowed 1 l-nitropropane,l-n-butane,

-n-pentane. to erlter a stream of 50% n1tr1c and vapor preheated to XXIU Hams, nimwm HNOL" Nitmmetham 260 C. at a rate such that the molar who of nitrite to XXII.-. Iso-amyl 111mm.-. HNOa... l-ni tr0-2-1nethylpropane, 2- nitric acid was maintained at 0.87. The gaseous mix- ;gg ggffg ture was fed to a reactor which consisted of a coiled aluminum tube immersed in a molten mixture of potassium and sodium nitrates heated to 400 C. The pressure These examples Illustrate the greater seleetlvlty Ph in the reactor was essentially atmospheric and the con- Vlded y the Process e Present lhvehtleh- For tact time was two seconds. The reaction products were stanc wh p te 15 hltleted according t e Pilot condensed and the nitroparaflin layer was separated from art Preeesses, 1h adltleh e the predllets Set forth In the aqueous layer. The nitroparaffin product was 83% amllle XXII, the p eh 0f y l it th d 17% it th 2-n1tro-3-methylbutane; 2-n1tro-2-methylbutane; 1-r11tro-3- meth lbutane' nitroethane' and Z-nitrobutane would be EXAMPLES 11 THROUGH XIII formeyd In an apparatus similar in all essentials to that described Various equivalents of the process in accordance with in Example I, nitric acid was reacted with isopropyl nitrite the invention are obvious, of course, to those skilled in and n-propyl nitrite in the molar ratio and under the the art and such equivalents are to be included within the conditions set forth hereinbelow in Table I. scope of the present invention.

Table I Nitrite HNO3 Mol ratio '1 0 Oil Nitrite Nitro- Nitro- Percent Percent Example Nitrite feed feed nitrite to recov. reeov. methane ethane 2-11itroconv. on yield on (g.) (g.) HNOg (g.) (g) (g.) (g.) propane HNO; nitrite Preheat React.

II Is0propyl 25.8 20 .90 240 268 9 6.85 1. 37 2.2 111 (10 24.4 21 .82 254 325 3.5 3.1 1.08 1.50

4e. 4 40. 5 .81 255 872 3. 0 .55 4; 5. 3 e7. 5 5s. 0 .85 254 421 7. 5 1.10 8. 30 10. 0 87. 4 30. 0 .88 244 353 8. 5 4. 79 8. 55 11.2 33. e 82. 0 .74 255 379 5. 5 1. 01 9. 5 l3. 3 44. 8 36. 5 .87 258 400 13.3 2. 81 22. 1 26. 9 45. 7 32.0 1. 01 253 428 9. 0 1. 11 19. 1 10. 3 54. 2 37. 0 1. 04 252 325 10.0 .97 11.3 11. 1 63. 5 1.12 258 415 13.0 .55 10.8 9. 7 53. 3 40 95 251 414 6. 0 .28 4. 0 4. 9 .4 400 *none *All oxidized.

EXAMPLE XIV It is claimed:

In an apparatus, similar in all essentials to that de- A e e fer e Selectlve p e l h 0f pf scribed in Example I, nitrogen dioxide preheated to 227 affihs Comprlslhg Teaehhg an alkyl hltrlte W1th a hltl'atlhg u C u a e a I Q C. was mixed wath liquid isopropyl n1tr1te and passed agent t a temperature of at 169st about 240 to P through the reactor at a temperature of 258 C. The (11196 hltroperathh and fee'eveflhg the P mole ratio was 0.95. After the reaction products were 50 T Process of 013111} 1 wherein t hh condensed the nitroparafiin in the organic layer was found hlttatlhg agent are reacted 111 a molar who of the hltrlte to be Substantially nitromethane to the nitratlng agent of from about 0.521 to 2.5:1.

3. The process of claim 1 wherein the nitrite is r0 1 EXAMPLES XV THROUGH XVII nitrite. P W In an pp t Similat h essentials to h flescrihed 4. The process of claim 3 wherein the nitrating agent in Example I, nitrogen d1ox1de was reacted W1th 1sopropyl i it i id nitrite and n-propyl nitrite in the molar ratio and under 5. The process of claim 3 wherein the nitrating agent the conditions set forth hereinbelow in Table II. EX- is N0 ample XIV is included in Table II for comparison. 6. A process for the selective production of nitro- Table II Percent conv. Percent yield M01 ratlo T 011 N01 011 nitrite Run Nitrite Nitrite NO: nitrite Oil NM, NE, nI nil'so P fed, g. fed, g. N02 rec., g. g. g. trate, g. nitrate Pre React NPs Nitrate NPs Nitrate XV Isopropyl. 20.3 11.0 .95 222 225 14.5 2.9 .28 8.1 XVI do 18.6 11.0 .87 225 242 12.8 7,3 35 2M XIV d0 20.3 11.0 .95 227 258 11.5 8.0 2.5 13.6 XVIL. n-PropyL- 23.4 11.0 1.10 220 253 10.0 9.5 5.2 15.4

paraffins comprising reacting an alkyl nitrite with nitric acid at a temperature from about 260 to 450 C. to produce nitroparaifin, and recovering. the nitroparafiins.

7. The process of claim 6 wherein the temperature is from about 375 to 425 C.

8. The process of claim 6 wherein the nitrite and nitric acid are reacted in a molar ratio of the nitrite to nitric acid from about 0.5 :1 to 25:1, and at a pressure from about atmospheric pressure up to about 15 atmospheres.

9. The process of claim 8 wherein the reactants are reacted at a contact time from about 0.2 to 20 seconds.

10. A process for the selective production of nitroparaflins comprising reacting an alkyl nitrite with N0 at a temperature from about 240 to 325 C. to produce nitroparafiin and recovering. the nitroparaflin.

11. A process for the selective production of nitromethane which comprises reacting an alkyl nitrite having from about 2 to 10 carbon atoms with a nitrating agent at an elevated temperature from about 240 to 450 C. in a molar ratio of nitrite to nitrating agent of from about 0.5 to 2.5 :1, recovering gaseous products including nitromethane from the reaction zone, and separating the nitromethane from the gaseous products.

12. A process as defined in claim 11 wherein the nitrite is n-propyl nitrite and nitroethane is also recovered from the gaseous products.

No references cited.

CARL D. QUARFORTH, Primary Examiner. 

1. A PROCESS FOR THE SELECTIVE PRODUCTION OF NITROPARAFFINS COMPRISING REACTING AN ALKYL NITRITE WITH A NITRATING AGENT AT A TEMPERATURE OF AT LEAST ABOUT 240*C. TO PRODUCE NITROPARAFFIN AND RECOVERING THE NITROPARAFFINS. 